Downtown Storm-water Management

Storm-water Management

The project at 211 Rigsbee demonstrates properly planned and installed green roofs can be compatible with historic preservation. It also demonstrates the potential for green roofs to contribute to storm-water management in the area.

Durham’s city center sits on the watershed boundary between the Jordan Lake and Falls Lake reservoirs, major sources of drinking water for the Triangle. Pollution carried by storm water has impaired the lakes, which are subject to North Carolina state rules for reducing pollutants and nutrients in the Neuse River basin and the Pamlico Sound. Runoff from The Republik
Building goes into Ellerbe Creek, which has the highest population density of Durham’s urbanized watersheds and flows directly to Falls Lake.

Given its size and the specific Xero Flor system option installed, the green roof atop the building on Rigsbee can prevent more than 50,000 gallons of storm-water runoff annually.

“Given its size and the specific Xero Flor system option installed, the green roof atop the building on Rigsbee can prevent more than 50,000 gallons of storm-water runoff annually,” Rugh says.

Could the green roof at 211 Rigsbee signal the future of storm-water management for Durham’s downtown? Peter Raabe, North Carolina conservation director for American Rivers, the nation’s leading river conservation organization, hopes so. “Our office in Durham is on the fifth floor of the Snow Building on Main Street. Looking out my window during storms, I see the rain pounding on the roofs of downtown buildings and surging into the streets. That runoff then rushes through the city’s storm-water drains that flow right into the creeks that feed the Falls and Jordan reservoirs,” Raabe explains. “This inspired a vision: what if some of those buildings had green roofs?”

According to an analysis conducted by American Rivers, there are 777 buildings in the downtown district with a total of nearly 5.2 million square feet of rooftops. Annual runoff from those rooftops tops 140 million gallons. With the area’s annual precipitation—and a green roof water retention efficiency rate of 75 percent (based on the technical specifications of the system atop The Republik Building)—every square foot of green roof in Durham could prevent about 20 to 23 gallons of storm-water runoff annually. Thus, if 25 percent of the roof surfaces downtown were covered by green roof assemblies similar to those on The Republik Building, runoff in downtown Durham could be reduced by an estimated 27 to 29 million gallons (approximately 20 percent) annually.

Accessible by an external roof ladder, The Republik Building’s green roof is not open to the public. However, XFA takes potential clients on the roof to show them the vegetated system and explain how it works.

“As a forward-thinking company known for innovation, The Republik wanted to lead the way with the first green roof on a historic building within the downtown district,” West says. “Other business owners and real-estate developers can now see how practical and beneficial a green roof can be. I am convinced more green roofs will be going up in downtown Durham.”

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November/December 2017 issue

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